| ACID | atomicity, consistency, isolation, durability |
| ACM | Association for Computing Machinery |
| AES | Advanced Encryption Standard |
| API | application programming interface |
| APPC | Advanced Peer-to-Peer Communication |
| AS/400 | Application System/400 |
| ASCII | American Standard Code for Information Interchange |
| ASN | Abstract Syntax Notation |
| ASN.1 | ASN 1 |
| ATM | automatic teller machine |
| AWT | Abstract Windowing Toolkit |
| AuthML | Authentication Markup Language |